The relationship between the level of carbon dioxide in the expired air or breath of a patient being resuscitated and the patient's circulatory status was the subject of experimental studies recently conducted and reported by Drs. Lepilian, Vasilyev, Bildinov and Rostovtseva, in a report entitled "End-Tidal Carbon Dioxide as a Noninvasive Monitor of Circulatory Status During Cardiopulmonary Resuscitation: A Preliminary Clinical Study" which was published in Critical Care Medicine Volume 15, No. 10, (1987). The studies were conducted on four patients during controlled ventilation, six to eight hours after aortocoronary bypass surgery. Each patient was mechanically ventilated with an oxygen-air mixture at an inspired oxygen fraction of 0.4. Expiratory carbon dioxide was monitored continuously with an infrared carbon dioxide analyzer. The report concluded that end tidal carbon dioxide concentration measurements taken during controlled ventilation of a patient experiencing acute circulatory failure can be used as an indirect noninvasive monitoring tool to assess the patient's circulatory status during cardiopulmonary resuscitation (CPR).
In view of this relationship between circulatory status and the level of carbon dioxide present in a patient's breath, it would be desirable if a device were available that is readily attachable to existing CPR equipment used by paramedics in the field. Such a device would preferably enable paramedics administering CPR to readily determine the level of carbon dioxide in a patient's breath. If the level of CO.sub.2 in the patient's breath were to drop below 1% "a level determined to be critical for adequate resuscitation" such a device would preferably promptly alert the paramedic to such, thereby providing the paramedics with more time (i.e., much needed time) to take whatever steps are necessary to save the patient's life.
U.S. Pat. No. 4,691,701 to Williams discloses a device which enables a paramedic to determine whether a patient's trachea has been properly intubated with an endotracheal tube (i.e., has the endotracheal tube been properly inserted into the trachea and not the esophagus). The device utilizes a chemical indicator which changes color when exposed to carbon dioxide. The device is added to an anaesthetic circuit and one expiration by the patient will instantly change the color of the indicator, thereby indicating that the trachea has been properly intubated, especially in conjunction with other signs.
Mine Safety Appliances brochure number 470243 discloses a device referred to as a dosimeter tube for detecting the presence of carbon dioxide in a mine. The dosimeter tube contains an acid base indicator which slowly changes color along the length of a tube when the end of the tube is broken, thereby exposing the indicator to carbon dioxide in the mine. The speed at which the indicator changes colors is proportional to the level of carbon dioxide in the mine. Accordingly, a high level of carbon dioxide in the mine will cause the indicator to change color along the length of the tube more quickly than a low level will. In determining such level, the miner measures the length of the indicator stain which has changed color and the period of time that has passed since the tube was broken. The miner then resorts to a precalibrated graph wherein the precise level is indicated as a function of stain length and time.
Other devices for carbon dioxide detection are disclosed in U.S. Pat. Nos. 4,619,269, 4,346,584 and 4,366,821.
While the aforementioned devices undoubtedly work as intended, there remains a need for a device that will enable paramedics to monitor the circulatory status of a patient being resuscitated in the field. Such a device would preferably be portable and readily attachable to existing equipment used by paramedics in the field.